Concern over the ozone depletion potential of certain halocarbons has resulted in a search for alternative compounds having lower ozone depletion potentials. Recently the long-term environmental effects of chlorofluorocarbons and even hydrochlorofluorocarbons have come under substantial scientific scrutiny, because it has been postulated that these materials decompose in the stratosphere, under the influence of ultraviolet radiation, to release chlorine atoms. Chlorine atoms are theorized to undergo chemical reaction in the stratosphere, which could deplete the stratospheric ozone layer, which shields the earth from harmful ultraviolet radiation. A substantial reduction of stratospheric ozone could have a serious deleterious impact on the quality, of life on earth.
There is a continuing need in this art for new materials having new combinations of properties for use in the aforementioned applications. In view of the potential environmental problem associated with stratospheric ozone depletion, there is a particular need for new materials possessing properties which make them useful in the subject applications and which are also potentially environmentally safe.
There is a limit to the number of single fluorinated hydrocarbon substances which could be candidates as environmentally safe materials. Mixtures of known materials, however, might be used if the desired combination of properties could be found in a given mixture. Also, certain .types of compositions can be formulated that are quite useful due to the temperature glide created through the heat exchangers, that is, the difference in the inlet and outlet temperatures of heat exchangers. These compositions exhibit novel properties that can be useful in increasing the energy efficiency of refrigeration equipment.
Fluorinated hydrocarbons have many uses, one of which is as a refrigerant. In refrigeration applications, a refrigerant is often lost during operation through leaks in shaft seals, hose connections, solder joints, and broken lines. In addition, the refrigerant may be released to the atmosphere during maintenance procedures on refrigeration equipment. Accordingly, it is desirable, when possible, to use a single fluorinated hydrocarbon, an azeotrope, or a near azeotropic composition that includes one or more fluorinated hydrocarbons as a refrigerant.
Fluorinated hydrocarbons may also be used as a cleaning agent or solvent to clean, for example, electronic circuit boards. Electronic components are soldered to circuit boards by coating the entire circuit side of the board with flux and thereafter passing the flux-coated board over preheaters and through molten solder. The flux cleans the conductive metal parts and promotes solder fusion, but leave residues on the circuit boards that must be removed with a cleaning agent.
Preferably, cleaning agents should have a low boiling point, non-flammability, low toxicity, and high solvency power so that flux and flux-residues can be removed without damaging the substrate being cleaned. Further, it is desirable that cleaning agents that include a fluorinated hydrocarbon be near azeotropic so that they do not tend to fractionate upon boiling or evaporation. If the cleaning agent were not near azeotropic, the more volatile components of the cleaning agent would preferentially evaporate, and the cleaning agent could become flammable or could have less-desirable solvency, properties, such as lower rosin flux solvency and lower inertness toward the electrical components being cleaned. The near azeotropic property is also desirable in vapor degreasing operations because the cleaning agent is generally redistilled and reused for final rinse cleaning.
Near azeotropic compositions of fluorinated hydrocarbons are also useful as blowing agents in the manufacture of close-cell polyurethane, phenolic and thermoplastic foams. Insulating foams require blowing agents not only to foam the polymer, but more importantly to utilize the low vapor thermal conductivity of the blowing agents, which is an important characteristic for insulation value.
Aerosol products employ both single component fluorinated hydrocarbons and near azeotropic compositions of fluorinated hydrocarbons as propellant vapor pressure attenuators in aerosol systems. Near azeotropic mixtures, with their essentially constant compositions and vapor pressures, are useful as solvents and propellants in aerosols.
Near azeotropic compositions that include fluorinated hydrocarbons are also useful as heat transfer media, gaseous dielectrics, fire extinguishing agents, power cycle working fluids such as for heat pumps, inert media for polymerization reactions, fluids for removing particulates from metal surfaces, and as carrier fluids that may be used, for example, to place a fine film of lubricant on metal parts.
Near azeotropic compositions that include fluorinated hydrocarbons are further useful as buffing abrasive detergents to remove buffing abrasive compounds from polished surfaces such as metal, as displacement drying agents for removing water such as from jewelry, or metal parts, as resist-developers in conventional circuit manufacturing techniques employing chlorine-type developing agents, and as strippers for photoresists when used with, for example, a chlorohydrocarbon such as 1,1,1-trichloroethane or trichloroethylene.